Combine all ingredients in a cocktail shaker. Add ice and shake until well chilled. Strain into a chilled coupe glass and garnish with a lemon twist and rim sugar, if desired.
Notes
After making the cocktail, you can adjust the level of sweet and sour, adding more of either element until it's to your liking.
Freshly squeezed lemon juice is a must. One lemon will yield enough juice for 2-3 cocktails, depending on its size and juiciness.
Peel off the twist before cutting the fruit to juice it.